The fifth generation of mobile telecommunications and wireless technology is not yet fully defined but is currently in an advanced draft stage within 3GPP. It includes work on 5G New Radio (NR) Access Technology. LTE terminology is used in this disclosure in a forward looking sense, to include equivalent 5G entities or functionalities although a different term is specified in 5G. A general description of the agreements on 5G New Radio (NR) Access Technology so far is contained in 3GPP TR 38.802 V0.3.0 (2016-10), of which a draft version has been published as R1-1610848. Final specifications may be published inter alia in the future 3GPP TS 38.2** series.”
In a wireless communication system, a wireless device, such as a user equipment or UE, needs to be able to receive and measure various common control signals. As an example, NR defines at least two types of synchronization signals NR-PSS, used at least for initial symbol boundary synchronization to the NR cell, and NR-SSS, used at least for detection of NR cell ID or at least part of NR cell ID. NR-SSS detection may typically be based on the fixed time/freq. relationship with NR-PSS resource position irrespective of duplex mode and beam operation type at least within a given frequency range and CP overhead. NR further defines at least one common control signals as the broadcast channel: NR-PBCH. NR-PBCH decoding may be based on the fixed relationship with NR-PSS and/or NR-SSS resource position, irrespective of duplex mode used and beam operation type used, at least within a given frequency range and CP overhead. PSS, SSS and/or PBCH may be transmitted within a synchronization signal ‘SS block’. One or multiple ‘SS block(s)’ may compose an ‘SS burst’. One or multiple ‘SS burst(s)’ may compose a ‘SS burst set’.
From 3GPP RAN1 specification perspective, the NR air interface defines at least one periodicity of the SS burst set.
A network node typically communicate in the wireless communication network by using one or more sets of radio resources selected from a total set of radio resources, e.g. resource blocks of a carrier or bandwidth. Common control signals may be repeated or duplicated using a particular subcarrier spacing. In an example using 3GPP NR, at least one subcarrier spacing for each synchronization signal, e.g. NR PSS, SSS, PBCH, is predefined in the 3GPP specification for a given frequency range. If multiple antenna beams are used to transmit the one or more control signals, at least the time index of SS-block is indicated to the UE. For the purpose of initial access by a UE, the UE can assume a control signal using radio resources corresponding to a specific subcarrier spacing of NR-PSS/SSS in a given frequency band given by the 3GPP specification. In a further example using 3GPP NR, the transmission of SS burst sets are periodic. For the purpose of initial access by a UE, the UE may assume a default periodicity of SS burst set transmission for a given carrier frequency, e.g. given by the 3GPP specification.
A first problem with conventional solutions is that the wireless device, e.g. a sub-band UE, may only be capable of or configured to receiving only to receive only some or a subset of transmission bandwidth of the serving network node. A second problem is that the wireless device may only be capable of or be configured to use a subset of the numerologies transmitted by the network node. Since the different numerologies may be FDM or TDM multiplexed, this means that there may be certain time intervals, or certain frequency ranges used by the network node for transmission of common control signals which the UE is not able to receive. A further problem is that the wireless device needs to be able to receive and measure various common control signals from a neighboring cell in the wireless communication system or network, e.g. to detect a cell prior to reporting, or prior to reselecting to the cell, or when the device is first powered on and needs to find a suitable cell to access.
Some conventional systems solve this by applying predetermined density or predetermined duplication of the control signals in the time or the frequency domain. Duplication could involve either transmitting identical symbols at different times or on different sub-carriers or the duplication could involve transmitting modified symbols at different times and frequencies where the means of modifying the common control signals in the duplication process is known to the UE.
A problem with applying predetermined density or predetermined level of duplication is that the transmission of common control signals constitutes a large overhead. Such signals are typically transmitted over the entire coverage area of a cell so may not be beam-formed and/or may need to be transmitted with high power. Transmitting duplicates of common control signals thus has a high cost in terms of resources consumed, which reduces the available network capacity, throughput etc.
Thus there is a need to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.